William is 68 years old and Ben is 20 years old. How many years will it take until William is only 3 times as old as Ben?
We can use the given information to write down an equation about how many years it will take. Let $y$ be the number of years that it will take. In $y$ years, William will be $68 + y$ years old and Ben will be $20 + y$ years old. At that time, William will be 3 times as old as Ben. Writing this information as an equation, we get: $68 + y = 3 (20 + y)$ Simplifying the right side of this equation, we get: $68 + y = 60 + 3 y$ Solving for $y$ , we get: $2 y = 8$ $y = 4$.